Install Windows after Ubuntu is installed

If one has Ubuntu already installed, and then Windows is installed on a different partition, they will notice that grub will be messed up. Ubuntu won’t be found anymore.
Here are the steps to safely do this:

1. Firstly, the data should be backed up. Whenever a new OS is installed, mistakes are easily made.
2. Boot the Ubuntu desktop CD, resize Ubuntu’s partition to make space for Windows. The resulting partition must be a NTFS partition. (Skip this if you already have a NTFS partition.
3. Then install Windows into the NTFS partitions.
4. Next boot into Ubuntu CD again and re-install grub. There is a visual tool that helps. It’s called boot-repair

sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update
sudo apt-get install -y boot-repair && boot-repair

Documentation on the tool can be found on Ubuntu boot repair documentation

The tool looks like this:

Thanks for the tip to bodhi.zazen